U0599 code meaning
Invalid Data Received From DC/DC Converter Control Module A
Network system Generic code U05xx codes Check engine light
What U0599 means
On start-stop vehicles a DC/DC converter can hold the 12 V supply for sensitive electronics while the starter pulls the voltage down; on hybrids it feeds the 12 V network from the high-voltage battery. GM's 2025 engine tables check the converter's output voltage and crank-control messages for alive counter, protection value and checksum errors and set U0599, Type B, after 8 failures in 18 samples with at least 11 V for 5 s. GM bulletin 20-NA-191 for the 2020 Cadillac CT4 and CT5 with auto start/stop shows the code set falsely: the ECM miscalculated the protection value during cranking without boost, disabled start-stop on the first failure and lit the MIL on the second; an ECM reprogram fixed it. FCA lists U0599 for the 2019 Cherokee V6 ESS; Ford's 2014 list has it without MIL.
U0599 at a glance
- Check engine lightYes, usually on
- Emissions testCan fail
- Limp modeNot expected
- Repair difficultyMedium
- Typical labor0.3 to 2 hours
- Clears after repairAfter a drive cycle
Symptoms of U0599
- Auto start/stop disabled
- Check engine light after repeated failures
Common causes of U0599
- Most likelyEngine controller software miscalculating the converter's protection value (GM 20-NA-191)
- PossibleDC/DC converter A electronics faulty
- Less likelyWeak 12 V battery causing deep voltage dips during cranking
Check the most likely causes first. Replacing parts by guesswork is the most expensive way to clear a code.
Parts involved
Dc dc converter module a
What each part of U0599 means
| U | Network system: communication between the control modules (CAN bus). |
| 0 | Generic code: it means the same on every make (SAE standard). |
| 99 | The exact fault in that area. |
What to do next
- Note U0599 and any other codes stored with it: several codes together often point to one cause.
- Check for loose connectors and damaged wiring around the parts the code names.
- Check open recalls for your car: some faults are fixed for free by the dealer. Enter your VIN.
- Clear the code only after the repair. If it comes back, the fault is still there.
Buying a used car? Scan it for stored codes before you pay. A recently cleared memory can hide a problem.
Questions about U0599
What does U0599 mean?
U0599 means "Invalid Data Received From DC/DC Converter Control Module A". On start-stop vehicles a DC/DC converter can hold the 12 V supply for sensitive electronics while the starter pulls the voltage down; on hybrids it feeds the 12 V network from the high-voltage battery. It is a generic code, so it means the same on every make.
Is it safe to drive with U0599?
Usually yes, for a short time, if the check engine light is steady and the car drives normally. If the light flashes or the car runs badly, stop and have it checked.
Will U0599 fail an emissions test?
Yes, it can. U0599 is emissions-related, so most inspection programs fail a car while it is stored or while the check engine light is on.
How hard is U0599 to fix?
Difficulty: medium. A typical repair takes 0.3 to 2 hours of work. This is a job for a workshop.
Will U0599 clear itself after the repair?
After the repair the car has to complete a drive cycle (a mix of city and highway driving) before the test runs again. Until then the readiness monitor shows "not ready", which can fail an inspection.